Poly(arylene sulfides) (hereinafter abbreviated as “PASs”) represented by poly(phenylene sulfide) (hereinafter abbreviated as “PPS”) are engineering plastics excellent in heat resistance, chemical resistance, flame retardancy, mechanical properties, electrical properties, dimensional stability and the like. The PASs are commonly used in a wide variety of fields such as electrical and electronic equipments and automotive equipments because they can be molded or formed into various kinds of molded or formed products, films, sheets, fibers, etc. by general melt processing techniques such as extrusion molding, injection molding and compression molding.
As a typical production process of a PAS, is known a process in which a sulfur source is reacted with a dihalo-aromatic compound in an organic amide solvent such as N-methyl-2-pyrrolidone. There is known a method of using an alkali metal hydrosulfide and an alkali metal hydroxide in combination as materials for a sulfur source. According to this method, however, the organic amide solvent is easy to be decomposed because the alkali metal hydroxide is used at a high concentration in the polymerization reaction. In addition, decomposition products form the cause of side reactions. For example, when N-methyl-2-pyrrolidone is used as an organic amide solvent, it is decomposed by the alkali metal hydroxide present at a high concentration to form a salt of a methylaminoalkylcarboxylic acid, which causes a side reaction. When a decomposition produce of the organic amide solvent is formed, it is difficult to control the side reaction by the decomposition product.
There have heretofore been proposed processes for producing a PAS, in the terminal of which a functional group has been introduced, by utilizing the fact that an alicyclic amide compound is decomposed by an alkali metal hydroxide to form a compound having a hydrolyzed structure (for example, Japanese Patent Application Laid-Open Nos. 2001-40090 and 2001-181394). Japanese Patent Application Laid-Open No. 2001-40090 describes a production process of a PAS, comprising reacting a polyhalo-aromatic compound, an alicyclic amide compound and an alkali metal hydroxide in the presence of water to hydrolyze the alicyclic amide compound, and then adding a sulfidating agent (i.e., an alkali metal hydrosulfide and/or an alkali metal sulfide) into the system to conduct polymerization. Japanese Patent Application Laid-Open No. 2001-40090 describes the fact that a PAS containing a carboxyalkylamino group of a structure that the alicyclic amide compound is hydrolyzed was obtained by this production process.
According to this process, a functional group can be introduced into a terminal of the PAS, but a side reaction is easy to take place, and the content of low-boiling impurities in the PAS formed is increased. As a result, when the PAS obtained by the above-described process is subjected to melt processing, a great amount of gasses are generated to clog an exhaust line in a melt-processing apparatus or facilitate production of voids in a molded or formed product. When the voids are produced in the molded product, the physical properties and surface properties thereof are deteriorated.
The above-described tendency may be generally observed not only in the production process described in the above document, but also in the case where an alkali metal hydrosulfide is used as a sulfur source, and an alkali metal hydroxide is used at a higher molar ratio than the alkali metal hydrosulfide for the purpose of providing a PAS having a high melt viscosity. On the other hand, when the alkali metal hydroxide is used at a lower molar ratio than the alkali metal hydrosulfide, the polymerization reaction system becomes unstable, and so the decomposition reaction is caused to easily progress. In any event, in conventional production processes, a molar ration of the alkali metal hydroxide to the alkali metal hydrosulfide is made excessively high in a polymerization reaction to conduct the polymerization reaction, so that side reactions are easy to progress, and difficulty is encountered on production of a high-purity PAS at high yield.
Specific examples are additionally mentioned. There have heretofore been proposed production processes of PAS, in which an alkali metal hydrosulfide, an alkali metal hydroxide and a polyhalo-aromatic compound are reacted by 2 stages (for example, Japanese Patent Application Laid-Open Nos. 2-302436 and 5-271414). In Japanese Patent Application Laid-Open No. 2-302436, it is described that the amount of the alkali metal hydroxide used is within a range of 0.7 to 1.3 mol, preferably 0.9 to 1.1 mol per mol of the alkali metal hydrosulfide. In Examples of Japanese Patent Application Laid-Open No. 2-302436, is shown an experimental example that 0.92 mol of sodium hydroxide was mixed at a time with 1 mol of sodium hydrosulfide to use it. Japanese Patent Application Laid-Open No. 5-271414 also discloses a like technical matter. According to these processes, however, it is difficult to efficiently advance the polymerization reaction while inhibiting decomposition reactions and side reactions.
There has heretofore been proposed a production process of poly(p-phenylene sulfide), in which a molar ratio of an alkali metal hydroxide to an alkali metal hydrogensulfide is controlled to 0.80:1 to 0.98:1 to conduct polymerization by one stage (for example, Japanese Patent Publication No. 6-51792). According to this process, however, decomposition reactions are easy to occur, and difficulty is encountered on stably performing a polymerization reaction because the ratio of the alkali metal hydroxide to the alkali metal hydrogensulfide (i.e., alkali metal hydrosulfide) is too low.
There has been proposed a production process of PAS, in which an alkali metal hydroxide is used in a proportion amounting to at most 1 mol per mol of an alkali metal hydrosulfide to conduct polymerization by one stage (for example, Japanese Patent Application Laid-Open No. 2001-181394). There has also been proposed a production process of PAS by one stage by using an alkali metal hydrosulfide and an alkali metal hydroxide to specify a molar ratio between the respective components (for example, Japanese Patent Application Laid-Open No. 2-160834). There has further been proposed a process for producing PAS by one stage by controlling the amount of an alkali metal hydroxide added to 0.3 to 4 mol per mol of an alkali metal hydrosulfide (for example, Japanese Patent Publication No. 6-51793). However, these processes also involve the same problems as in the processes disclosed in Japanese Patent Application Laid-Open Nos. 2-302436 and 5-271414.
Further, the melt viscosities of conventional PASs obtained by polymerizing the sulfur source and the dihalo-aromatic compound in the presence of the alkali metal hydroxide in the organic amide solvent markedly vary with difference in washing method after polymerization or difference in resin pH even when the PASs are the same kind. In particular, a PAS whose pH is alkaline after washing undergoes a sort of ionic crosslinking by an alkali metal ion such as a sodium ion, and so its melt viscosity becomes markedly high compared with an acidic PAS. When such a PAS is subjected to melt processing such as melt spinning, it is difficult to stably conduct an operation due to variations of melt viscosity during the processing.